Implicit DRX cycle length adjustment control in LTE_active mode

ABSTRACT

A method for controlling discontinuous reception in a wireless transmit/receive unit includes defining a plurality of DRX levels, wherein each DRX level includes a respective DRX cycle length and transitioning between DRX levels based on a set of criteria. The transitioning may be triggered by implicit rules.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/664,002, filed Mar. 20, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/535,915, filed Jun. 28, 2012, which issued asU.S. Pat. No. 9,014,032 on Apr. 21, 2015, which is a continuation ofU.S. patent application Ser. No. 12/022,233, filed Jan. 30, 2008, whichissued as U.S. Pat. No. 8,238,260 on Aug. 7, 2012, which claims thebenefit of U.S. Provisional Patent Application No. 60/887,276, filedJan. 30, 2007, the contents of which are incorporated by referenceherein.

FIELD OF DISCLOSURE

The present invention is in the field of wireless communications.

BACKGROUND

A goal of the Third Generation Partnership Project (3GPP) Long TermEvolution (LTE) program is to develop new technology, new architectureand new methods for settings and configurations in wirelesscommunication systems in order to improve spectral efficiency, reducelatency and better utilize the radio resource to bring faster userexperiences and richer applications and services to users with lowercosts.

In a typical LTE network, a wireless transmit/receive unit (WTRU) mayoperate in a number of modes. While in LTE_ACTIVE mode, the WTRU mayoperate in a discontinuous reception (DRX) mode. DRX mode allows theWTRU to operate in a low power, or sleep mode, for a preset time, andthen switch to a full power, or awake, mode for another preset time inorder to reduce battery consumption. The DRX cycle lengths are generallyconfigured by the enhanced universal terrestrial radio access network(E-UTRAN) so that an enhanced Node B (eNB) and the WTRU are synchronizedon a consistent sleep and wake-up cycle.

Live traffic situations and WTRU mobility may require frequentadjustment of the DRX cycle length in order to balance systemperformance, WTRU performance and WTRU power savings. However, relyingonly on WTRU/E-UTRAN signaling to make the fine DRX cycle adjustment mayincur a heavy system and WTRU signaling load.

Implicit rules for DRX cycle length adjustment may be used for smoothLTE_ACTIVE DRX operations to reduce battery power consumption while noteffecting system or WTRU performance issues. Implicit rules may assistthe implicit DRX cycle length transitions between the WTRU and theE-UTRAN without using excessive explicit signaling.

SUMMARY

A method and apparatus are disclosed for controlling discontinuousreception in a WTRU. The method may include defining a plurality of DRXlevels, wherein each DRX level includes a respective DRX cycle length,and transitioning between DRX levels based on a set of criteria.Transitioning may be triggered by implicit rules. Triggering may beinvoked by a measurement event, a timer, a counter or a downlinkcommand, for example. The transitions between DRX states may occurwithout explicit signaling.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings wherein:

FIG. 1 shows a wireless communications system in accordance with oneembodiment;

FIG. 2 is a functional block diagram of a WTRU and an e Node B (eNB) inaccordance with one embodiment; and

FIG. 3 is a state diagram of implicit DRX transition in accordance withone embodiment;

FIG. 4 is a signal flow diagram for implicit DRX transition inaccordance with one embodiment;

FIG. 5 is a flow diagram for a method of implicit DRX signaling inaccordance with one embodiment;

FIG. 6 is a flow diagram for a method of implicit DRX signaling inaccordance with another embodiment;

FIG. 7 is a flow diagram for a method of implicit DRX signaling inaccordance with an alternative embodiment; and

FIG. 8 is a flow diagram for a method of implicit DRX signaling inaccordance with another alternative embodiment.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows a wireless communication system 100 in accordance with oneembodiment. The system 100 includes a plurality of WTRUs 110 and an eNB120. As shown in FIG. 1, the WTRUs 110 are in communication with the eNB120. Although three WTRUs 110 and one eNB 120 are shown in FIG. 1, itshould be noted that any combination of wireless and wired devices maybe included in the wireless communication system 100. The eNB 120 andthe WTRUs 110 may communicate while in DRX mode and may have coordinatedDRX cycles.

FIG. 2 is a functional block diagram 200 of a WTRU 110 and the eNB 120of the wireless communication system 100 of FIG. 1. As shown in FIG. 1,the WTRU 110 is in communication with the eNB 120. Both WTRU 110 and eNB120 may operate in DRX mode.

In addition to the components that may be found in a typical WTRU, theWTRU 110 includes a processor 215, a receiver 216, a transmitter 217,and an antenna 218. The processor 215 may be configured to adjust DRXcycle length as necessary. The receiver 216 and the transmitter 217 arein communication with the processor 215. The antenna 218 is incommunication with both the receiver 216 and the transmitter 217 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical eNB 120,the eNB 120 includes a processor 225, a receiver 226, a transmitter 227,and an antenna 228. The processor 225 is configured to communicate withthe receiver 226 and transmitter 227 to adjust DRX cycles as necessary.The receiver 226 and the transmitter 227 are in communication with theprocessor 225. The antenna 228 is in communication with both thereceiver 226 and the transmitter 227 to facilitate the transmission andreception of wireless data.

In order to improve battery life, but not limit the eNB 120 and WTRU 110performance, transitions between DRX cycle length states may be definedimplicitly, rather than explicitly. The implicit rules may beimplemented at the radio resource control (RRC) and the medium accesscontrol (MAC) levels while the WTRU 110 is in a LTE_ACTIVE DRX state.

Approximately half of WTRU 110 to eNB 120 interaction involves WTRU 110requests and reports and eNB 120 responses while the WTRU 110 is inLTE_ACTIVE DRX mode. When the WTRU 110 measures a particular scenario,measurement events may be reported to the eNB 120, and the eNB 120 mayrespond to the situation by commanding the WTRU 110 to start a newservice, mobility activity, and the like. If the downlink commandtransmission or reception is limited by a relatively long DRX cyclelength, WTRU 110 and eNB 120 system performance during LTE_ACTIVE DRXmode may suffer. However, certain measurement events may make goodcandidates for the anticipated network downlink commands.

FIG. 3 shows an implicit DRX transition state machine 300 in accordancewith one embodiment. The state machine 300, as well as associatedtransition mechanisms and parameter values, may be configured by the eNB(120 of FIG. 1). The state machine 300 may have a life span, alsoconfigured by the eNB 120. Each state may be applied at the WTRU (110 ofFIG. 1) and at the eNB 120, so that operation is consistent andsynchronized. At each defined and configured DRX state, a different DRXcycle length is associated with both the WTRU 110 and the eNB 120operations.

The DRX cycle length transition rules may be based on WTRU 110 and eNB120 experiences. Given a certain elapsed time, or a given set ofmeasurement values, the WTRU 110 and the eNB 120 may learn and predicttraffic patterns. These learned and predicted traffic patterns may besuperimposed on a general model for a state machine, resulting in theDRX state machine 300 for a WTRU 110/eNB 120 system that permitsimplicit transition operation and consistent DRX actions for both theWTRU 110 and the eNB 120. The eNB 120 can prescribe DRX states forservice and mobility conditions with the potential for continuousimprovement and learned traffic patterns upon every invocation.

FIG. 3 shows 3 defined DRX levels, 302, 304, 306 and an undefined DRXlevel 308. In DRX level 3 306, the WTRU 110 is operating in a normal DRXcycle. The actual length of the normal state may be defined by the eNB120. DRX level 2 304 is a shorter cycle length than DRX level 3 306, andis associated with more frequent activity than normal. The eNB 120 mayalso define the cycle length for DRX level 2 304, and may also set a“resume” period. A resume period is a length of time in which there areno new transmissions and after which the WTRU 110 may return to DRXlevel 3 306 operation, unless the WTRU 110 is commanded to do otherwise.

DRX level 1 302 has the shortest DRX cycle length, and may be used by aWTRU 110 or eNB 120 to handle predicted immediate downlink commands andwhen uplink traffic patterns are recognized by the WTRU 110 and the eNB120 as requiring immediate downlink action, such as during a handoverevent, for example.

A DRX level n 308 may be configured with longer DRX cycles than that forthe DRX Level 3 306. The eNB 120 can redefine the DRX cycle lengths foreach state at the end of the DRX configuration life span but may observea DRX cycle length rule that lower level DRX states have shorter DRXlengths.

For a WTRU 110 at DRX level 3 306, a timer or counter trigger may bedefined to trigger a transition to DRX Level 2 304 if the eNB 120determines that the WTRU 110 should periodically transition to a “busy”cycle to check downlink data. This may be considered a trigger based ona measurement event. Another trigger based on a measurement event canalso be defined to transition a WTRU 110 from DRX level-3 306 to DRXLevel 1 when a traffic volume event on a certain radio beareraccumulating a larger amount of uplink data than a threshold is reportedand an anticipated Radio Bearer (RB) Reconfiguration command isimminent.

If the WTRU 110 in DRX Level 1 302 state receives a RB Reconfigurationcommand, the current DRX Level 1 state is over. If the WTRU 110 at DRXLevel 1 state 302 does not receive the anticipated command for thedefined “resume period”, it can go back to its original DRX state andresume the power saving DRX cycle. Regular timers and counters may beused during a DRX mode to trigger the implicit DRX cycle lengthtransition. The choice between the timers and counters and the values ofthe timers or counters may be based on learned traffic patterns andmodels with respect to the mobility and/or service state of the WTRU 110at a particular time while the WTRU 110 is in LTE_ACTIVE DRX mode. Thetimer or counter triggers may be used as transition triggers to bring upthe DRX cycle length as well as to bring down the DRX cycle length asthe DRX state changes.

The eNB 120 may configure DRX parameters based on a network trafficmonitoring operation and analysis. Several methods exist to select theparameter values, such as by including a default system value set thatis defined for implicit DRX transition operation. Optionally, theparameters may be published in system information broadcasts, or theycan be determined by the eNB 120 from time to time and loaded to aparticular WTRU 110 via higher layer signaling before an intended DRXmode period.

Transitions between different states may be signaled in an informationelement (IE). An example of a skeleton for signaling an implicit DRXcycle transition is shown in Table 1. As shown in Table 1, the ImplicitDRX Transition List is mandatory and is limited to a value indicating amaximum number of DRX states.

The DRX cycle length IE is mandatory, and is an integer. The triggermechanisms are optional, and may be a trigger to move up a DRX statelevel, or move down a DRX state level. The Implicit DRX Transitionconfigured life Span IE is mandatory, and sets the resume period fornon-normal states. The Initial DRX state is optional, and may set theDRX state of the WTRU 110 at start-up.

To aid with easier DRX cycle length transition and maintain DRX cyclelength synchronization between the WTRU 110 and the eNB 120, the DRXcycle length definition may be given as a function of the shortest DRXbase number (L). Then various DRX length values may be:DRX-cycle-len=L×2^(n),  Equation (1)where n=0, 1, 2 . . . such that the resulting DRX-cycle-len does notexceed a maximum DRX cycle length. The shortest DRX cycle lengthpossible occurs when n=0, and is a fraction of a longer DRX cyclelength.

The use of DRX cycle lengths that are multiples of each other reducesthe probability that DRX periods may be mismatched and provides anefficient mechanism to resynchronize DRX periods between the WTRU 110and eNB 120. When DRX periods are defined as multiples of each other,and when DRX periods become mismatched between the WTRU 110 and the eNB120, each entity can determine the period of the other by increasing ordecreasing the cycle length to determine the period being used by theother entity, and resynchronizing the entities accordingly.

Typically, a WTRU 110 in DRX Level 1 302 may count n times before ittransits back to the original DRX state. The default may be given as:n=(Level-k DRX Cycle Length or original DRX cycle length)/Level-1 DRXCycle Length; where Level-k cycle length is the length of the DRX cyclebefore the WTRU 110 enters DRX Level 1 302. Alternatively, the networkmay configure n for the “resume method”.

TABLE 1 Information Type and Element/Group name Need Multi referenceSemantics description Implicit DRX Transition MP maxDRX List states(TBD) >DRX Cycle Length MP Integer (TBD) >Trigger-UP-1 OP Trigger Tonext upper level Mechanism DRX State A.B.C.D >Trigger-UP-2 OP TriggerUsed by Level-1 for Mechanism resume A.B.C.D >Trigger-Down-1 OP TriggerTo next lower level Mechanism DRX state A.B.C.D >Trigger-Down-2 OPTrigger To Level-1 trigger Mechanism A.B.C.D Implicit DRX Transition MPTBD Time in seconds configured life span Initial DRX state OP TBD

Transitions from state to state may be initiated by a trigger. Table 2shows an example of transition trigger IEs. Each of the IEs ismandatory, except for the resume period. The Transition Trigger ismandatory and is specified by the network if specified as shown inTable 1. The CHOICE mechanism allows the network to configure the WTRU110 for implicit DRX operational triggers. The trigger Timer value maybe in units of absolute time, LTE frames or transmission time intervals(TTIs) and is used to monitor or regulate ON and OFF periods for networksignaling channel activities or data channel activities for the WTRU110. The Counter values may be an integer value used to check theoccurrences of certain trigger events. The measurement event mayenumerate the event that causes the trigger. The resume period may be atime period given in seconds, DRX cycles, or some other value, thatdenotes the total time a WTRU 110 may remain in an elevated statewithout receiving a command to move back to normal state.

TABLE 2 Information Element/ Type and Semantics Group name Need Multireference description Transition Trigger MP CHOICE MPmechanism >Timer >> Timer Value MP Integer TBD >Counter >> Counts MPInteger TBD >Measurement Event >> measurement MP Enumerated Event-Id(TBD) >resume period CV- TBD Could be default in Trigger- Level-1 State.UP-2 Default is to stay n Level-1 cycles so the total length isequivalent to its original DRX state DRX length

FIG. 4 is a signal flow diagram for implicit DRX transition 400 inaccordance with one embodiment. A WTRU 402 may receive an RRC message oran IE 406 from the E-UTRAN 404 that triggers the WTRU 402 to enter DRXmode. The WTRU 402 may enter DRX mode 408 at a default level which maybe a normal cycle length DRX level 3 (306 of FIG. 3). Both the WTRU 402and the E-UTRAN 404 enter DRX mode (408, 410 respectively). The WTRU 402may receive another RRC message or IE 412 that triggers the WTRU 402 toenter a faster DRX cycle mode (DRX level 1 302 of FIG. 3). The WTRU 402and the E-UTRAN 404 enter the DRX level 1 (414, 416 respectively). AWTRU timer 418, synchronized with an E-UTRAN timer (not shown), expires.As the timers are synchronized, no notice of timer expiration isrequired. The expiration of the timer 418 triggers the WTRU 402 and theE-UTRAN 404 to return to normal DRX level. The WTRU 402 returns 422 toDRX level-3 306 at the same time that the E-UTRAN 404 returns 424 to DRXlevel-3 306.

FIG. 5 is a flow diagram of a method of implicit signaling 500 inaccordance with one embodiment. At step 502 the WTRU is in normaloperating mode, or Level-3. At step 504, the WTRU checks to see if atimer has timed-out, or a trigger has been received that would force theWTRU to move to another DRX state. If no, at step 506, the WTRU remainsin normal state. If the WTRU detects a time out signal or a trigger atstep 504, at step 508, the WTRU determines if it should move to DRXLevel 1 or DRX level 2. If the WTRU determines that the trigger is alevel-2 trigger, at step 510 the WTRU moves to DRX Level 2. At step 512,the WTRU determines that the resume period has ended, and returns to DRXlevel-3. If, however, the WTRU, at step 508, determines that it receiveda level 1 trigger, at step 514, the WTRU goes into a DRX level 1. Atstep, 516, the WTRU determines if it has received a Radio BearerReconfiguration message. If not, the WTRU, at step 518, waits for theresume period to end and returns to normal operation at step 522. If,however, at step 516, the WTRU receives a radio bearer reconfiguremessage, at step 520, the WTRU returns to normal DRX cycle operation.

FIG. 6 is a flow diagram of an implicit DRX method 600 in accordancewith another embodiment. At step 602, the WTRU is in normal or DRXLevel-3 mode. At step 604, the WTRU conducts a traffic volumemeasurement. At step 606, the WTRU compares the traffic volumemeasurement with a threshold. If the volume is below the threshold, atstep 608, the WTRU takes no action and remains in DRX Level-3 mode.However, if, at step 606, the WTRU determines that the traffic is abovea threshold, at step 610, the WTRU changes mode to a shorter DRX cycle.Based on the traffic, the new DRX mode may be DRX level-2 or DRXlevel-1. At step 612, the WTRU determines if a command or message hasbeen received. If yes, at step 614, the WTRU returns to Level-3 mode. Ifnot, at step 616 the WTRU waits the resume period before returning tolevel-3 mode at step 618. Optionally, the E-UTRAN may determine thetraffic volume measurement reporting threshold level for DRX statetransition triggering. Once the defined traffic volume measurement eventoccurs, the DRX state transition is triggered.

While in LTE_ACTIVE DRX mode, a WTRU may perform traffic volumemeasurements for uplink traffic. The E-UTRAN may configure the WTRU toreport the events on threshold crossing. Based on learned trafficpatterns, the E-UTRAN determines that there is a large volume change,which may means that an RB addition, an RB reconfiguration or an RBrelease command is imminent. Therefore, the traffic volume event reportsmay be used as implicit DRX transition triggers. For example, a largevolume change may be used to trigger the WTRU into the shortest DRXcycle (DRX level 1, 302 of FIG. 3, for example) in order to receive thenetwork command. The network, when receiving the predeterminedmeasurement event, may determine the WTRU's DRX state via implicit DRXtransition rules and either sends the anticipated command to the WTRU orwait for the WTRU to return to its previous DRX state with the specified“resume period”.

By way of another example, the WTRU, while in LTE_ACTIVE mode, may useconfigured handover measurements. Certain measurement event reports mayindicate that a handover (HO) command is imminent for intra-frequency,inter-frequency or an inter-radio access technology (RAT) handover.Depending on handover measurement events, certain other measurementevents may act as triggers for DRX transition control. FIG. 7 is a flowdiagram of a method of implicit DRX signaling 700 in accordance with analternative embodiment. At step 702, the WTRU is in normal DRX level 3state. At step 704, the WTRU determines that a serving cell measurementis below a threshold. The WTRU may then determine that anintra-frequency measurement is high 706, meaning that an intra-frequencyneighbor is measuring as the best cell. Alternatively, the WTRU maydetermine that an inter-frequency band measures to be the best 708. Asanother alternative, the WTRU may determine that a non-LTE systemmeasures the best 710.

At step 712, the WTRU, due to the measurements, may anticipate ahandover command. At step 714, the WTRU reports the measurement event.This may invoke, at step 716, an implicit DRX transition trigger thatcauses the WTRU to go to a Level-1 DRX state in order to receive thepossible handover command from the network. At step 718, the WTRUreceives the handover command. At step 720, the WTRU transitions back toits original DRX state.

FIG. 8 is a flow diagram of a method of implicit DRX cycle signaling 800in accordance with yet another embodiment. At step 802, the WTRU islevel-1 mode. At step 804, the WTRU begins to monitor a Level 1/Level 2control channel to intercept anticipated downlink commands. At step 806,the WTRU determines if an anticipated network command is received. Ifreceived, at step 808, the WTRU will follow the command to end the DRXmode or will receive instruction on the next DRX activity with thecommand. If the command is not received, at step 810, the WTRUtransitions back to its original DRX state before entering the Level-1state.

Although the features and elements are described in the embodiments inparticular combinations, each feature or element can be used alonewithout the other features and elements or in various combinations withor without other features and elements. The methods or flow chartsprovided may be implemented in a computer program, software, or firmwaretangibly embodied in a computer-readable storage medium for execution bya general purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

What is claimed is:
 1. A method implemented by a wirelesstransmit/receive unit (WTRU), the method comprising: the WTRU receivinga discontinuous reception (DRX) configuration in a radio resourcecontrol (RRC) message, the DRX configuration comprising a first DRXcycle length, a second DRX cycle length, and a value for a WTRU timerused to trigger a transition from the first DRX cycle length to thesecond DRX cycle length, wherein the second DRX cycle length is amultiple of the first DRX cycle length; the WTRU performing DRX usingthe second DRX cycle length; the WTRU receiving a trigger from a basestation; the WTRU performing DRX using the first DRX cycle length basedon receiving the trigger; the WTRU starting the WTRU timer uponbeginning DRX operation using the first DRX cycle length; the WTRUdetermining that the WTRU timer has expired; and the WTRU transitioningfrom the first DRX cycle length to the second DRX cycle length inresponse to the WTRU determining that the WTRU timer has expired.
 2. Themethod as in claim 1, wherein the second DRX cycle length is an integerpower of two of the first DRX cycle length.
 3. The method as in claim 2,wherein the first and second DRX cycle lengths are selected from a setof DRX cycle lengths given by the equation DRX-cycle-len=L×2^(n) wheren=0, 1, 2, . . . and L is the first DRX cycle length.
 4. The method asin claim 1, wherein the WTRU timer is synchronized with a base stationtimer.
 5. The method as in claim 1, wherein the WTRU timer isimplemented as a counter.
 6. The method as in claim 1, wherein the valueof the WTRU timer is signaled as a number of DRX cycles.
 7. A wirelesstransmit/receive unit (WTRU) comprising a processor and memoryconfigured to: receive a discontinuous reception (DRX) configuration ina radio resource control (RRC) message, the DRX configuration comprisinga first DRX cycle length, a second DRX cycle length, and a value for aWTRU timer used to trigger a transition from the first DRX cycle lengthto the second DRX cycle length; perform DRX using the second DRX cyclelength; receive a trigger from a base station; perform DRX using thefirst DRX cycle length based on receiving the trigger; start the WTRUtimer upon beginning DRX operation using the first DRX cycle length;determine that the WTRU timer has expired; and transition from the firstDRX cycle length to the second DRX cycle length in response to theexpiration of the WTRU timer, wherein the second DRX cycle length is amultiple of the first DRX cycle length.
 8. The WTRU as in claim 7,wherein the second DRX cycle length is an integer power of two of thefirst DRX cycle length.
 9. The WTRU as in claim 8, wherein the first andsecond DRX cycle lengths are selected from a set of DRX cycle lengthsgiven by the equation DRX-cycle-len=L×2^(n) where n=0, 1, 2, . . . and Lis the first DRX cycle length.
 10. The WTRU as in claim 7, wherein theWTRU timer is synchronized with a base station timer.
 11. The WTRU as inclaim 7, wherein the WTRU timer is implemented as a counter.
 12. TheWTRU as in claim 7, wherein the value of the WTRU timer is signaled as anumber of DRX cycles.
 13. A wireless transmit/receive unit (WTRU)comprising a processor and memory configured to: receive a discontinuousreception (DRX) configuration in a radio resource control (RRC) message,the DRX configuration comprising a first DRX cycle length, a second DRXcycle length, and a value for a WTRU timer used to trigger a transitionfrom the first DRX cycle length to the second DRX cycle length; receivea first trigger from a base station, the first trigger indicating thatthe WTRU should perform DRX using the second DRX cycle length; performDRX using the second DRX cycle length based on receiving the firsttrigger; receive a second trigger from the base station, the secondtrigger indicating that the WTRU should perform DRX using the first DRXcycle length; perform DRX using the first DRX cycle length based onreceiving the second trigger; start the WTRU timer upon beginning DRXoperation using the first DRX cycle length; determine that the WTRUtimer has expired; and transition from the first DRX cycle length to thesecond DRX cycle length in response to the expiration of the WTRU timer,wherein the second DRX cycle length is a multiple of the first DRX cyclelength.
 14. The WTRU as in claim 13, wherein the second DRX cycle lengthis an integer power of two of the first DRX cycle length.
 15. The WTRUas in claim 14, wherein the first and second DRX cycle lengths areselected from a set of DRX cycle lengths given by the equationDRX-cycle-len=L×2^(n) where n=0, 1, 2, . . . and L is the first DRXcycle length.
 16. The WTRU as in claim 13, wherein the WTRU timer issynchronized with a base station timer.
 17. The WTRU as in claim 13,wherein the WTRU timer is implemented as a counter.
 18. The WTRU as inclaim 13, wherein the value of the WTRU timer is signaled as a number ofDRX cycles.
 19. The method as in claim 1, further comprising: the WTRUreceiving a second trigger from the base station, the second triggerindicating that the WTRU should perform DRX using the second DRX cyclelength; and the WTRU performing DRX using the second DRX cycle lengthbased on receiving the second trigger.
 20. The WTRU as in claim 7,wherein the processor and memory are further configured to: receive asecond trigger from the base station, the second trigger indicating thatthe WTRU should perform DRX using the second DRX cycle length; andperform DRX using the second DRX cycle length based on receiving thesecond trigger.